The heat sensing cable of the present invention is of the same general type as described in prior U.S. Pat. Nos. 3,257,530; 3,701,985; and 3,950,746, all of which issued in the name of the present inventor. The heat sensing cable of the invention, similar to the cable described in the aforesaid patents, is intended to be used either indoors or outdoors and in conjunction with homes, or large or small industrial facilities, underground as in mines, in the frozen North, or in the hottest deserts. The heat sensing cable of the invention has the advantage of being unaffected by extremes in weather conditions. The cable may also be used in all types of environmental-contaminated areas without affecting its long life and efficient operation.
The cable of the invention is primarily intended to function as a single or multi-stage heat sensing device. However, as will be described, it can also be used to perform additional functions while still performing its primary functions. These additional functions may include, for example, anti-intrusion and break-in warnings, monitoring unattended equipment, signalling emergency calls, and voice communication either when used as an antenna for radio communication in underground installations or by the use of one of the multi-cables for above-ground use, all these additional functions being performed without in any way affecting its primary function as a multi-stage heat sensing device. In addition, the heat sensing cable of the invention is capable of providing for the detection and location of a broken span at any point along its length.
As mentioned briefly above, the heat sensing cable of the invention may be constructed to provide a sequence of alarms. Specifically, the cable may detect fire in a very early stage by the inclusion of smoke or products of combustion detectors at any point along its length, connected to specific wires of the multi-conductor cable. This early warning may be used to sound only a local alarm to permit local personnel to take immediate action, and thus prevent that alarm from being transmitted to the central fire station if the fire is small enough to be extinguished locally. A second alarm will sound directly into the Fire Station if the fire is unchecked and the temperature should reach 125.degree. F. or 155.degree. F. Likewise, as also mentioned, if the fire should still persist, and get out of control, the cable will initiate a third alarm when the temperature reaches a higher level such as in the range, for example, of 175.degree. F.-225.degree. F., and this alarm is also transmitted to the local fire station, where the signals would be identified and their exact location would be indicated, so that appropriate action could be taken.
The various combinations of cables of the invention are installed in continuous spans of any desired length to suit any particular application, and each span is placed under tension by appropriate means, which will be described subsequently. The spans, for example, may extend five feet to 500 feet, or more. A single circuit of the cable may be, for example, up to 20 miles long. Normal spans in warehouses and most installations would be tensioned by use of a tension spring or springs, to supply the desired tension, whereas, in underground installations the Tension Arm, as described in U.S. Pat. No. 3,950,746 would be used; and for outdoor use where it is desired to use very long spans and expansion and contraction due to ambient temperature ranges may change the length of the cable, also the length of the cable will vary due to the wind causing the cable to bow, in this case weights and pulleys must be used to keep the span under constant tension.
An important feature of the heat sensing cable of the present invention, and an advantage of the present cable over the prior art types, is that it requires only one manufacturing operation, and this is the extrusion of a single conductor plastic-covered cable. Two or three or more types of single conductor cables may be readily manufactured, each having varying gauges of conductors and varying ranges of thermal-responsive plastic insulating material, depending on the requirements. The finished cable may then be wound from single-conductor cable reels into a two-conductor, three-conductor, etc. cable, with the individual cables having either the same thermal-responsive plastic insulating material, or a combination of two or more types of thermal-responsive plastic insulating materials.
Polarity indicia of the conductors, and appropriate identification markings, may be applied at the time of twisting the single-conductor cables into the multi-conductor heat-sensing cable. The multi-conductor heat-sensing cable may include, for example, one or two conductors coated with Teflon, or other suitable non-thermal-responsive high temperature resistant insulating material, and wound either in the same direction as the thermal-responsive conductors, or in the opposite direction. The non-thermal-responsive conductors may be used for communication purposes, and its insulation is intended to withstand as high temperatures as possible, to enable its use after the other thermal-responsive cables have shorted together due to the heat of the fire.
An advantage of the heat-sensitive cable of the present invention is that it may be produced more simply and economically than the prior art heat-sensitive cable, and in that it is better subject to quality control. Also, large stocks of the various required types of the multi-conductor heat-sensitive cables of the invention are not necessary, since the single-conductor cables may be stocked, and wound together into various combinations, as the particular needs arise. For example, for most purposes, only three types of single-conductor thermal-responsive cable need be stocked, representing, for example, a low temperature range insulation, a medium temperature range insulation, and a high temperature range insulation. One or two non-thermal-responsive cables could be included and used, for example, voice communication. A summary of the combination of such a multi-conductor cable and its uses might be as follows:
__________________________________________________________________________ No. of Single Conductor Cable Operation Conduc- Low Med. High SERVICE Heat tors Range Range Range Teflon Fire Emerg. Voice Range __________________________________________________________________________ 2 2 -- -- -- .sqroot. -- -- Low 2 -- 2 -- -- .sqroot. -- -- Med. 2 -- -- 2 -- .sqroot. -- -- High 3 2 -- -- 1 .sqroot. -- .sqroot. Low 3 -- 2 -- 1 .sqroot. -- .sqroot. Med. 3 2 1 -- -- 2 stage .sqroot. -- Low, Med. 3 -- 2 1 -- 2 stage .sqroot. -- Med. High 3 -- -- 2 1 .sqroot. -- .sqroot. High 4 2 1 1 -- 3 stage .sqroot. -- Low, Med. High 4 2 1 -- 1 2 stage .sqroot. .sqroot. Low, Med. 4 -- 2 1 1 2 stage .sqroot. .sqroot. Med. High 4 2 -- -- 2 .sqroot. -- .sqroot. Low 5 2 1 1 1 3 stage .sqroot. .sqroot. Low, Med. High 6 2 1 1 2 3 stage .sqroot. .sqroot. Low, Med. High __________________________________________________________________________